Multipoint Light Emitting Optical Fibers (MPF) has been recently demonstrated as a versatile tool for spatially
addressable optogenetics experiments. Their fabrication has been possible thanks to a number of key microfabrication
technologies, in particular the unique nanofabrication capabilities of a Focused Ion Beam. This work provides the
complete description of MPF fabrication, detailing the optimization process for each fabrication step.

We experimentally demonstrate the possibility to implement an optical bio-sensing platform based on the shift of the
plasmonic band edge of a 2D-periodic metal grating. Several 2D arrangements of square gold patches on a silicon
substrate were fabricated using electron beam lithography and then optically characterized in reflection. We show that
the presence of a small quantity of analyte, i.e. isopropyl alcohol, deposited on the sensor surface causes a dramatic red
shift of the plasmonic band edge associated with the leaky surface mode of the grating/analyte interface, reaching
sensitivity values of ~650nm/RIU. At the same time, dark field microscopy measurements show that the spectral shift of
the plasmonic band edge may also be detected by observing a change in the color of the diffracted field. Calculations of
both the spectral shift and the diffracted spectra variations match the experimental results very well, providing an
efficient mean for the design of sensing platforms based on color observation.

In this paper we describe the fabrication of a periodic, two-dimensional arrangement of gold square patches on a Silicon
substrate, and highlight technological limitations due to the roughness of the metal layer. Scanning Electron Microscope
(SEM) and Atomic Force Microscope analyses are also reported showing that the geometrical parameters obtained are
almost identical to the nominal parameters of the simulated structure.
The device is functionalized by means of a conjugated rigid thiol forming a very dense, closely packed, reproducible 18
Å–thick, self-assembled monolayer. The nonlinear response of the 2D array is characterized by means of a micro-Raman spectrometer and it is compared with a conventional plasmonic platform consisting of a gold nano-particles ensemble on Silicon substrate, revealing a dramatic improvement in the Raman signal. The SERS response is empirically investigated using a laser source operating in the visible range at 633 nm. SERS mapping and estimation of the provided SERS enhancement factor (EF) are carried out to evaluate their effectiveness, stability and reproducibility as SERS substrate.
Moreover, we take advantage of the simple geometry of this 2D array to investigate the dependence of the SERS
response on the number of total illuminated nano-patches.

Colloidal nanocrystals, i.e. quantum dots synthesized trough wet-chemistry approaches, are promising nanoparticles for
photonic applications and, remarkably, their quantum nature makes them very promising for single photon emission at
room temperature. In this work we describe two approaches to engineer the emission properties of these nanoemitters in
terms of radiative lifetime and photon polarization, drawing a viable strategy for their exploitation as room-temperature
single photon sources for quantum information and quantum telecommunications.

In this paper we present a reliable process to fabricate GaN/AlGaN one dimensional photonic crystal (1D-PhC)
microcavities with nonlinear optical properties. We used a heterostructure with a GaN layer embedded between two
AlGaN/GaN Distributed Bragg Reflectors on sapphire substrate, designed to generate a λ= 800 nm frequency downconverted
signal (χ(2) effect) from an incident pump signal at λ= 400 nm. The heterostructure was epitaxially grown by
metal organic chemical vapour deposition (MOCVD) and integrates a properly designed 1D-PhC grating, which
amplifies the signal by exploiting the double effect of cavity resonance and non linear GaN enhancement. The integrated
1D-PhC microcavity was fabricate combing a high resolution e-beam writing with a deep etching technique. For the
pattern transfer we used ~ 170 nm layer Cr metal etch mask obtained by means of high quality lift-off technique based
on the use of bi-layer resist (PMMA/MMA). At the same time, plasma conditions have been optimized in order to
achieve deeply etched structures (depth over 1 micron) with a good verticality of the sidewalls (very close to 90°).
Gratings with well controlled sizes (periods of 150 nm, 230 nm and 400 nm respectively) were achieved after the pattern
is transferred to the GaN/AlGaN heterostructure.

We analyze in this work the second harmonic amplification of χ(2) nonlinear process in membrane type GaAs circular
photonic crystal. This unconventional kind of photonic crystal is well suited for the generation of whispering gallery
modes due to the circular symmetric periodic pattern. The Gaussian beam of a fundamental pump signal at 1.55 μm
defines a whispering gallery mode resonance and generates a second harmonic mode at 0.775 μm in the central missing
hole micro-cavity. The periodic pattern and the micro-cavity are tailored and optimized in order to generate a second
harmonic conversion efficiency of 50 %. We predict the resonances by an accurate 2D time domain model including χ(2)
nonlinearity and also by a 3D Finite Element Method FEM. Moreover, by using a 3D membrane configuration, we
predict a quality factor of the second harmonic mode of the order of 35000.

We present in this work the scalar potential formulation of second harmonic generation process in χ(2) nonlinear
analysis. This approach is intrinsically well suited to the application of the concept of circuit analysis and synthesis to
nonlinear optical problems, and represents a novel alternative method in the analysis of nonlinear optical waveguide, by
providing a good convergent numerical solution. The time domain modeling is applied to nonlinear waveguide with
dielectric discontinuities in the hypothesis of quasi phase matching condition in order to evaluate the conversion
efficiency of the second harmonic signal. With the introduction of the presented rigorous time domain method it is
possible to represent the physical phenomena such as light propagation and second harmonic generation process inside a
nonlinear optical device with a good convergent solution and low computational cost. Moreover, this powerful approach
minimizes the numerical error of the second derivatives of the Helmholtz wave equation through the generator
modeling. The novel simulation algorithm is based on nonlinear wave equations associated to the circuital approach
which considers the time-domain wave propagating in nonlinear transmission lines. The transmission lines represent the
propagating modes of the nonlinear optical waveguide. The application of quasi phase matching in high efficiency
second harmonic generation process is analyzed in this work. In particular we model the χ(2) non linear process in an
asymmetrical GaAs slab waveguide with nonlinear core and dielectric discontinuities: in the nonlinear planar
waveguides a fundamental mode at λ=1.55 μm is coupled to a second-harmonic mode (λ=0.775 μm) through an
appropriate nonlinear susceptibility coefficient. The novel method is also applied to three dimensional structures such as
ridge waveguides.

Theoretical analysis on second harmonic (SH) generation with phase matched grating in waveguide is presented from
the viewpoint of device design. Usually high intensity sources are necessary in order to observe a SH in a χ(2) nonlinear
structure. For this purpose, the novel proposed design takes into account a double grating effect which enhances the
guided SH signal along the waveguide. In the presented structure two grating are considered: the first grating,
considered at the interface between air and core, is designed in order to obtain an efficient SH conversion process by
considering the quasi phase matching (QPM) condition; the second grating, placed at the interface between the core and
the substrate region, increases the SH power along the propagation direction through the coupling with the substrate
modes generated by the diffraction effect. The novelty of this work is in the combined effect of the two gratings. The
grating lengths and periods are designed by considering the nonlinear coupled mode theory with the effective dielectric
constant (EDC) assumption. The analysis includes three dimensional (3D) cases where phase matching is involved, in
particular the model is applied to a GaAs/AlGAs waveguides with fundamental wavelength at λFU=1.55 μm and SH
signal at λSH =0.775 μm.

This work presents a detailed numerical Finite Element Method FEM modeling for passive optical components such as
photonic crystals (PhCs). The accurate modeling characterizes the PhCs structures by considering the field resonance
and the radiation behavior of the periodic pattern. The frequency responses at each side of the photonic crystal are
evaluated by considering the 3D periodic structure enclosed in a black box with six input/output ports. This scattering
matrix approach (SMA) is useful in order to evaluate in plane and vertical PhCs the resonance of the photonic crystal.
Through the analysis of all the frequency responses we characterize the passband regions and the stopband regions of
the PhC slab.

We report on the growth and characterization of low threshold 1.32-μm quantum dots (QDs) laser diodes. The quantum dot active region was optimised to get the highest photoluminescence emission and the lowest Full Width at Half Maximum (FWHM). From samples containing multilayer QDs and using the Limited-Area Photoluminescence (LAPL) technique we have shown that the gain of an N-layer structure is higher than N times that of a single layer. This enhancement is attributed to the increase of the quantum dot density in the upper layers and also to the use of the high growth temperature spacer layer. Broad area laser diodes were processed from the grown samples containing three layers of InAs QDs grown directly on GaAs and capped with 4-nm-thick InxGa1-xAs layer. Than measurements were performed at room temperature under pulsed excitation. The laser diodes operate at room temperature and emit between 1.29 and 1.32-μm which is beyond the strategic telecommunication wavelength. The characteristic temperature is around 80 K and very stable in the hole range of the operating temperature (from 0 to 90 °C). The internal quantum efficiency is 53% and the modal gain per QD layer was estimated to be ~ 6 cm-1. For an infinite cavity length a threshold current density of 8 A/cm2 per QD layer was obtained. From the calculation of the optical confinement of QDs, we have estimated a material gain of 1979 cm-1.

Colloidally synthesized CdSe/ZnS core/shell semiconductor nanocrystals (NCs) show highly efficient, narrow-width and size-tunable luminescence. Moreover, they can be incorporated in polymer matrices and deposited on solid substrates by means of spin-coating techniques. When embedded between two mirrors a NCs/polymer blends microcavity is realised, thus allowing to tailor the photoluminescence spectrum of these emitters. By virtue of the quantized photonic and electronic density of states, colloidal quantum dots embedded in a single mode vertical microcavity are good candidates for the fabrication of high-efficiency emitting devices with high spectral purity and directionality.
In this paper, we have applied a new organic-inorganic hybrid technology for the fabrication by imprint lithography (IL) of vertical microcavities that embed colloidal quantum dots.
Two dielectric distributed Bragg reflectors (DBR) are evaporated on two different substrates. The active organic layer (NCs/polymer blend) is spin coated on the first DBR, whereas a lithographic pattern is realized on the second DBR, used as the IL mold. The two parts are then assembled together in an IL process in order to create a vertical microcavity. The fine control of the thickness of the active material waveguide layer can be achieved through the mold patterning depth and the IL process parameters. All the fabrication steps have been engineered in order to decrease the thermal stress of the active layer.
The effectiveness of this technology is demonstrated by the room temperature photoluminescence (PL) spectra, recorded on the fabricated microcavity, which show a sharp emission peak with a line width of 4.15 nm.

In this paper we propose the design and the fabrication of 90° bend ridge waveguide (WG) assisted by a two-dimensional photonic crystal (2D-PC). 2D-PCs act as efficient mirrors along the boundaries of the bend ridge thus reducing the in-plane losses. The ridge waveguide consists of a 3 μm x 0.75 μm titanium dioxide core on a silica bottom cladding. The 2D-PC structure surrounding the bend waveguide is composed of a triangular array of circular dielectric pillars having a height of 0.75 μm. The titanium dioxide waveguiding core layer is covered with PMMA in order to create a quasi-symmetric structure. A photonic band gap centered around 1.3 μm is obtained by a PC radius r = 0.33a and lattice period a = 0.450 μm. The design of the whole structure is subsequently optimized by using a 3D Finite Difference Time Domain based computer code. The ridge waveguide assisted by a 2D-PC has been fabricated by using electron beam lithography and reactive ion etching. For the pattern transfer we have used about 50 nm thin layer Cr metal etch mask obtained by means of a lift-off technique based on the use of bi-layer resist (PMMA/MMA).
The presence of the 2D-PC around the bend waveguide leads to a sharp increase of the transmission efficiency around 1.3 μm for curvature radius of 2.5 μm. The bend transmission results to be in the range between 0.76 and 0.85 when the thickness of the ridge WG and of the 2D-PC pillars is between 0.75 and 1.3 μm. This value is more than twice with respect to the bend waveguide without 2D-PC.

In this work we present a method to obtain room temperature ground state emission beyond 1.3 μm from InGaAs QDs, grown by MOCVD, embedded directly into a binary GaAs matrix. The wavelength is tuned from 1.26 μm up to 1.33 μm by varying the V/III ratio during the growth of the GaAs cap layer, without using seeding layer or InGaAs wells. A line-shape narrowing (from 36 meV to 24 meV) and a strong reduction of the temperature dependent quenching of the emission (down to a factor 3 from 10K to 300K) are observed, that represent the best value reported for QD structures emitting at 1.3 μm.
The results are explained in term different morphological evolution and surface reconstruction undergone by the InGaAs islands during the GaAs overgrowth that result in larger QD size and in lower In-Ga intermixing. Indeed, cross sectional TEM images show an increase in the QD size of more than 30% with decreasing the AsH3 flow.
The overall strain reduction due to the use of the GaAs matrix allows the fabrication of highly efficient staked QD layers. The single and multiple QDs samples show a systematic increase of the emission intensity and similar spectral shape.

The trapping mechanisms at the origin of the persistent photocurrent effects in GaN-based devices have been studied on
different time scales by characterizing a low barrier metal-semiconductor-metal GaN-based photodetector in the
temperature range between room temperature and 500 K. The active material of the metal-semiconductor-metal device
consists of a thin film of GaN grown by metal organic chemical vapour deposition. The Arrhenius plots obtained by the
analysis of the decay times of the photocurrent as a function of the temperature on time scales from millisecond up to
hours allowed us to calculate the activation energies of the mechanisms responsible for the persistent photocurrent. The
activation energies derived from the decay times on the time scale of hours have been attributed to gallium vacancies
(VGa), gallium antisites (GaN) and carbon impurities, whereas GaN excitonic resonances resulted to be responsible for the
persistent photocurrent on the millisecond time scale. Finally, the influence of the decay times has been correlated with
the photocurrent gain of the device, which resulted to be as high as 4.1×105 at RT and 0.85×105 at 450 K.

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